Paper-based chemical assay devices with improved fluidic structures

A chemical assay device comprising:

• a first hydrophilic substrate having a first side and a second side, a predetermined length and width, and a thickness of not more than 1 millimeter;
• and
• a plurality of hydrophobic structures formed in the first hydrophilic substrate from a hydrophobic material, the hydrophobic material being selected from a group consisting of a wax and a phase change ink, each hydrophobic structure in the plurality of hydrophobic structures including the hydrophobic material extending from one arrangement in a plurality of arrangements of the hydrophobic material through substantially the thickness of the first hydrophilic substrate from the first side to the second side, each arrangement of the hydrophobic material being formed on only the first side of the first hydrophilic substrate prior to penetration of the hydrophobic material into the first hydrophilic substrate with a single shape and size, and a ratio of a maximum area for a largest hydrophobic structure in the plurality of hydrophobic structures to a minimum area for a smallest hydrophobic structure in the plurality of hydrophobic structures being less than 1.25.